planetarium

American  

[plan-i-tair-ee-uhm] / ˌplæn ɪˈtɛər i əm /

noun

planetariums, plural planetaria plural

1. an apparatus or model representing the planetary system.

2. a device that produces a representation of the heavens by the use of a number of moving projectors.

3. the building or room in which such a device is housed.

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planetarium British  

/ ˌplænɪˈtɛərɪəm /

noun

1. an instrument for simulating the apparent motions of the sun, moon, and planets against a background of stars by projecting images of these bodies onto the inside of a domed ceiling

2. a building in which such an instrument is housed

3. a model of the solar system, sometimes mechanized to show the relative motions of the planets

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Other Word Forms

Inflected Forms

noun

• planetaria
  plural
• planetariums
  plural

Etymology

Origin of planetarium

1765–75; < New Latin, noun use of neuter of Latin planētārius planetary; cf. -arium

Explanation

A planetarium is a theater where you can look at images of planets, stars, and other celestial bodies on the dome-shaped ceiling. Planetariums host school field trips by day, and can even host Pink Floyd laser light rock shows by night. Use the noun planetarium for the projector that shines light onto the surface of the building's dome, recreating solar systems and constellations — and also for the building itself, where such a show is put on. Because planetarium is a Modern Latin word (from the roots planeta, or "planet," and -arium, "a place for,"), its plural can be either planetariums or planetaria.

Example Sentences

A mobile planetarium allowing people to immerse themselves in the night sky has opened in Hull.

From BBC • Apr. 3, 2026

It added that they would create an "astronomical observatory, planetarium and visitor centre in the heart of the internationally-recognised Galloway Forest Dark Sky Park".

From BBC • Mar. 3, 2026

A 37-year-old convict, who had more than a year still to serve for theft, fled on November 14 during an outing with fellow prisoners to the city's planetarium.

From Barron's • Nov. 28, 2025

But while those groups seemed to want to soundtrack trippy shows in a planetarium, Tortoise typically favors concise, punchy tracks built around defined hooks.

From The Wall Street Journal • Oct. 28, 2025

She assured Mia that yes, Shaker schools were excellent—Pearl could enroll in AP classes in every subject; there were science labs, a planetarium, five languages she could learn.

From "Little Fires Everywhere" by Celeste Ng